Tan's simple HA questions

tanstaaf1

Member
How can I shield a control wire from a power wire if they *must* run some distance very closely in parallel?

I thought I'd use a generic topic title so I can hopefully reuse this thread as I come up with other questions that I don't think warrant a lot of response.
 

Guy Lavoie

Active Member
Some kind of metal sheathing could be added. Even something as simple as wrapping the control wire in aluminum foil and grounding it at one end might be all you need.
 

tanstaaf1

Member
Guy Lavoie said:
Some kind of metal sheathing could be added....
Thx. That is what I was thinking of doing - I was going to run the powerline in metal electrical conduit - but I didn't want to presume that would necessarily help shield the control line from magnetic flux (for all I knew, it might increase it somehow).
 

Guy Lavoie

Active Member
tanstaaf1 said:
...but I didn't want to presume that would necessarily help shield the control line from magnetic flux (for all I knew, it might increase it somehow).
If the conduit is not grounded, then that could happen. But grounding the conduit properly will have the effect of draining any induced noise to ground and preventing it from reaching the cable inside.
 

TCassio

Active Member
You can also run sheilded control wire (eaiser than condiut) just make sure you ground only 1 end of the shield.
 

upstatemike

Senior Member
How far is "some distance"? 10 feet? 300 feet?

Rules about running next to power wires usually refer to romex or other unshielded wires. You can go as far as you want next to grouned conduit or BX.

What is in the low voltage wire? Audio, fire alarm, or analog signals are sensitive to AC induction while thermostat, relay. doorbell, etc. are not.

As mentioned above, you can always use shielded wire for the low voltage line if you ground the shield at one end only (to avoid a ground loop).
 

tanstaaf1

Member
I'm putting in a small maybe 4" x 6" support post in the center of a large room and supplying power (for lamps) and control/data from 2 under-slab plastic contuits but switching to metal for the power over the critical foot or so where there will be proximity. This is open beam construction so I really can't make the support post bigger too easily.

I am thinking the post would be good for one of the maybe 4 touch screen interfaces I hope to have to control effectively all features of the HA and whole house audio. I might also put an intercom & network connection there. I'm planning on putting in 2 cat5 and probably 1 quad shielded coax (about all that will fit in the conduit).

In this particular application the wires will be maybe 3" apart but only for a foot or so; I asked the question in a general fashion so the answer would hopefully be applicable in some other cases where the parallel runs might be longer: 10 feet or more.

What is shielded cat5 called... just "shielded cat 5"? Where can I buy this, as I don't think they carry it at Home Depot?
 

upstatemike

Senior Member
It is known as STP (Shielded Twisted Pair) cabling as opposed to the commonly used UTP cabling (normal Cat-5).

For a 1 foot run at 3 inches of separation I wouldn't worry about it unless you are planning on super high current on the AC circuit. For 20A (12 ga) or smaller you won't induce enough noise into the Cat-5 to be a problem. Coax is already shielded so you are all set there.
 

jlehnert

Active Member
Agreed with upstatemike.

With that short amount of distance, and a regular 20 (or 15) amp circuit, you should have no problem.

A lot of the "keep LV 12" away from HV" mantra comes from the early days of UTP (10baseT) being installed in office buildings. Early versions of UTP + high voltage (and ofter electrically noisy) office circuits = trouble. The current state of the art is much more robust, and most of the time a several ft run together won't be a problem.
 

electron

Administrator
Staff member
I have many Cat5E (used for sensors, video, IR, ethernet, ...) drops running along power wiring, some up to 40ft, and I have 0 problems. I will try to keep things seperate in the future, but I didn't have a choice with this house, I am just surprised how well it works.
 

tanstaaf1

Member
electron said:
I have many Cat5E (used for sensors, video, IR, ethernet, ...) drops running along power wiring, some up to 40ft, and I have 0 problems. I will try to keep things seperate in the future, but I didn't have a choice with this house, I am just surprised how well it works.
You probably just saved me a ton of money and work. I was about to begin ripping out large amounts of wiring put in place by a non-HA saavy electrician because he ran it in way many places within inches of power line (I think he was thinking in terms of doorbells and alarm switches). Now, at least, I will try and test it out for adequacy before I just start yanking.

Also, presuming I have your attention, thanks for the great FAQ on cabling. Your comment in that FAQ that speaker wire is much more tolerant of nearby electrical because of the higher power in the speaker wire, saved me from ripping out a bunch of speaker wire which was similarly closely run in parallel.

This is also the first I heard of working around a potential problem with grounding of metal sheathing or conduit ("on one end only") and using STP wire. Perhaps well known to y'all, but I've not read it before - just lots and lots and lots of warning, now, about keeping 1 1/2 feet away unless crossing perpendicular. I've been critiquing my electrician for not having organized his electrical wires closer together so as to give me my 1 1/2 feet everywhere.
 

royalj7

Active Member
Tan,

It is always good practice to keep the low voltage wiring in a differnt stud bay than the power wiring. In new construction, there is no reason not to (other than ignorence by the electrician). In remodeling jobs, it becomes a lot harder, but still a something to aim for. The one area that you could see a differnce is if you are trying to run a 1000baseT network. You have to get alot of things right to get true gigabit speed and things like termination and bend radius are probably more important, but proximity to power will increase the noise and inturn the latency of the network. STP is rare in residential locations. As been said, running short distances parallel to 15 or 20A circuits is not normally going to cause a problem. One foot at three inches won't cause a problem, so feel free to disreguard the above section :ph34r:, just an FYI.

--Jamie
 

tanstaaf1

Member
royalj7 said:
...It is always good practice to keep the low voltage wiring in a differnt stud bay than the power wiring. ...The one area that you could see a differnce is if you are trying to run a 1000baseT network. You have to get alot of things right to get true gigabit speed and things like termination and bend radius are probably more important, but proximity to power will increase the noise and inturn the latency of the network.....
QUESTION #2: GETTING MAXIMUM NETWORK SPEED FOR YOUR DOLLAR/EFFORT.

Interesting that you brought up the topic of network speed, as I was just about to bring it up as another question. I've been reading the book "HTI+" (Home Technology Integration) and it says "A star ethernet may be slower than a bus ethernet, especially if there are many nodes on the network. This happens because the hub generates a lot of traffic that isn't used. Because it replicates all the data that it receives from any source and sends it to every node...packets from different nodes...collide with one another...the collision and replication of data transmissions slow down the network."

Getting maxium speed may not be an issue now, but if you want streaming high quality video and other future higher data applications, new networks should obviously push for maximum speed within budget constraints.

- How big a deal is this star vs bus issue when all the cat 5 is "home run" (presumably meaning you have a star)?

- What other factors should I be aware of that unnecessarily reduce future network speed?
 

WayneW

Senior Member
I think your information source is old. AFAIK, bus Ethernet went out with the coax, I think it was called 10base-2 and it was daisy chained.

The other key word is "hub". For anything with more than a few ports, I don't think hubs are easily available anymore. Everything big should be on a switch, which only sends traffic down the leg it needs to go. It doesn't broadcast to all legs like a hub did.
 
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